Changes done:

1. Add registers for R01_sig and R32_sig on FreeBSD/powerpc64le.
2. Add mozjs config and source files.
3. Rename src/checksum/power8/crc32.sx to src/checksum/power8/crc32.S.
   The reason is that Clang refuses to build .sx files and needs .S for assembly.
   This should also help building with Clang on other operating systems.
4. Clang doesn't have ppc-asm.h header. When building with Clang, use the
   bundled ppc-asm.h file from GCC (this is what upstream at https://github.com/antonblanchard/crc32-vpmsum does).
   This should also help building with Clang on other operating systems.

Original Description

MongoDB currently supports only Linux on ppc64le architecture. Supporting FreeBSD is trivial and has been implemented in https://github.com/mongodb/mongo/pull/1390

It's already committed in FreeBSD ports tree in databases/mongodb40, databases/mongodb42 and databases/mongodb44 ports.